1. Field of the Invention
The present invention relates to a keyboard device applied to a keyboard instrument, such as an electronic piano, and more particularly to a key support structure for pivotally supporting keys.
2. Description of the Related Art
Conventionally, there have been known, for example, keyboard devices disclosed in Japanese Laid-Open Patent Publications (Kokai) No. 2011-27854 and No. 2003-330450 filed by the present applicant. Each of the keyboard devices disclosed in Japanese Laid-Open Patent Publications (Kokai) No. 2011-27854 and No. 2003-330450 has a keyboard chassis and a plurality of keys including white keys and black keys. The keys each extend in a front-rear direction and are arranged in a left-right direction, with respective rear ends thereof pivotally supported on the keyboard chassis. Further, in each of the keyboard devices, the keyboard chassis and each of the keys are formed by injection-molding of predetermined synthetic resins, respectively. More specifically, an ABS resin is used for the keyboard chassis, and an AS resin which has a higher hardness than that of the ABS resin is used for the keys so as to prevent the keys from being easily scratched.
In the keyboard device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2011-27854, each key and the keyboard chassis are constructed as follows: The key has pivot shafts projecting outward from respective left and right sides of the rear end thereof. On the other hand, the keyboard chassis has a first support part which is arc-shaped for supporting the pivot shafts of the key. A pivot shaft bearing member having a second support part that cooperates with the first support part to constitute a bearing for the pivot shafts is removably mounted on the keyboard chassis with screws. According to the keyboard device constructed as above, it is possible to improve the ease of assembly during a manufacturing operation and disassembly during an operation for disposal, while ensuring stable pivotal motion of the keys.
On the other hand, in the keyboard device disposed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-330450, each key and the keyboard chassis are constructed as follows: The key has a top wall, which has a rear end cut out into a U shape, and left and right side walls, which have respective rear ends formed to largely protrude downward and have respective inner surfaces formed with protrusions opposed to each other. On the other hand, the keyboard chassis has a keyboard support part provided thereon on a key-by-key basis for supporting each key. The keyboard support part is formed therethrough with an engagement hole that extends in the left-right direction, for being engaged with the two protrusions of the rear ends of the side walls of the key, in their state inserted from the opposite sides of the keyboard support part. When mounting the key on the keyboard chassis, the rear end of the key is pressed toward the associated one of the keyboard support parts of the keyboard chassis, whereby the rear end of the key is elastically deformed such that the left and right side walls of the key are pushed laterally outward to increase spacing therebetween. Then, when the key is further pressed downward, the two protrusions are snap-fitted into the engagement hole of the keyboard support part through elastic return of the opposite side walls of the rear end of the key to their original state. According to the keyboard device constructed as above, it is possible to achieve reduction of manufacturing costs by reducing the number of component parts and that of assembly steps, while ensuring stable pivotal motion of the keys.
However, in the case of the keyboard device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2011-27854, it is required to attach the pivot shaft bearing member as a separate component part to the keyboard chassis, for supporting the associated key, and fix the same with screws, which causes an increase in the number of component parts and that of assembly steps. Further, if the pivot shaft bearing member is mounted on the keyboard chassis with a mounting error, the pivot shafts of the key are loosened, which is liable to generate noise during key depression. On the other hand, the keyboard device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-330450 makes it possible to reduce the number of component parts and that of assembly steps in comparison with the keyboard device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2011-27854, but since the key is made of the AS resin having a hard property because of the requirement of properties thereof as mentioned hereinabove, there is a fear that when attaching or removing the key to or from the keyboard chassis, if the left and right side walls of the rear end of the key are forcibly pushed laterally outward overcoming much difficulty in order to increase spacing therebetween, the side walls suffer damage, such as cracking. Further, there is a fear that when the keyboard is pushed forward due to an impact e.g. during transit, the side walls of the key are deformed in a direction of moving apart from each other, whereby the protrusions of the rear end are disengaged from the engagement hole of the keyboard support part.